1. Field of the Invention
The present invention relates to a musical tone signal generating apparatus for an electronic musical instrument and, more particularly, to a musical tone signal generating apparatus which can smoothly switch an output musical tone waveform in correspondence with a change in designated pitch.
2. Description of the Related Art
Conventionally, a musical tone signal generating apparatus of a waveform-data read type is known. In this apparatus, waveform data is read out from a waveform data memory storing digital waveform data and a musical tone is generated like in a PCM system on the basis of pitch data designated in accordance with a pitch designation operation by operating a pitch designation switch or the like. In an electronic musical instrument adopting a musical tone signal generating apparatus of this type, when a pitch of a musical tone in generation is to be smoothly changed, e.g., when a legato, a pitch bend operation, a portamento operation a slide (glissando) operation, or the like is executed, a pitch is changed by changing only a data reading speed (read frequency or an address increment speed) without changing waveform data read out from the waveform memory in correspondence with a musical tone in generation (a musical tone immediately before a pitch is changed).
However, when musical tones are generated by reading out one recorded waveform in correspondence with pitches over a wide range, tone colors cannot be naturally changed in correspondence with a compass of musical tones unlike in an acoustic musical or natural instrument in accordance with a change in pitch.
For example, when an instruction for producing a musical tone of a pitch C.sub.5 is issued by, e.g., the legato while a musical tone of a pitch C.sub.4 is read out and produced in a loop mode between loop start and end addresses, the same waveform data of the same loop portion as the pitch C.sub.4 is directly used, and a read speed (read frequency) is merely changed in correspondence with the pitch C.sub.5. Therefore, since waveform data before and after the legato is executed is left unchanged, a tone color is not naturally changed in correspondence with a compass unlike in an acoustic musical instrument. In particular, when a pitch is largely changed by, e.g., a pitch bend operation, an unnatural state is caused before and after a change in pitch.
In order to prevent a change unnatural in tone color according to a change in pitch, a method called multisampling has been used. In this method, a waveform corresponding to one tone color is sampled and prestored in a memory in units of predetermined ranges (e.g., one octave), and the stored waveform is selectively read out and generated in accordance with a designated pitch in a reproduction mode.
However, in a musical tone signal generating apparatus of this type, when a pitch is largely changed upon operation of a bender during generation of a musical tone, a tone color tends to be changed. When a pitch is changed beyond the predetermined range, a waveform in a higher or lower compass adjacent to a compass of a waveform in generation is read out in correspondence with the designated pitch, and the waveform before the pitch is changed is switched to the waveform of the adjacent range.
However, memory spaces for storing waveforms in units of tone ranges are independent of each other for each waveform of a range. Thus, when the waveforms are switched by changing addresses of independent memory spaces, the waveforms may become discontinuous. In practice, it is difficult to generate musical tones by connecting waveforms of adjacent tone ranges.
For example, when a tone generation instruction of a pitch C.sub.5 is issued by, e.g., the legato while a musical tone of a pitch C.sub.4 is read out and produced in a loop mode between loop start and end addresses, a read speed is immediately changed in correspondence with the pitch C.sub.5, and waveform data of the same loop portion as the pitch C.sub.4 is read out. Therefore, when a pitch is changed, since quite different waveform data is generated in a loop period, and the waveform data is read out, a musical tone of an unnecessary tone color is instantaneously generated.